658 research outputs found
Search for three alpha states around an O core in Si
We investigate the existence of weakly coupled gas-like states comprised of
three particles around an O core in Si. We calculate the
excited states in Si using the multi-configuration mixing method based
on the O + 3 cluster model. We also include the O +
C and Mg + basis wave functions prepared by the
generator coordinate method. To identify the gas-like states, we calculate the
isoscalar monopole transition strengths and the overlap of the obtained states
with the geometrical cluster wave function and the
Tohsaki-Horiuchi-Schuck-R\"{o}pke (THSR) wave function. The results show that
the obtained fourth and twelfth states significantly overlap with the THSR wave
function. These two states clearly coexist with the O + C cluster
states, emerging at similar energies. The calculated isoscalar monopole
strengths between those two states are significantly large, indicating that the
states are members of the excitation mode. Furthermore, the calculated
root-mean-squared (RMS) radii for these states also suggest that a layer of
gas-like three particles could exist around the surface of the
O core, which can be described as a "two-dimensional gas" in the
intermediate state before the Hoyle-like three states emerge.Comment: 5 pages, 3 figure
Enhanced excitation of Giant Pairing Vibrations in heavy-ion reactions induced by weakly-bound projectiles
The use of radioactive ion beams is shown to offer the possibility to study
collective pairing states at high excitation energy, which are not usually
accessible with stable projectiles because of large energy mismatch. In the
case of two-neutron stripping reactions induced by 6He, we predict a population
of the Giant Pairing Vibration in 208Pb or 116Sn with cross sections of the
order of a millibarn, dominating over the mismatched transition to the ground
state.Comment: 6 pages, 4 figure
Alpha-cluster Condensations in Nuclei and Experimental Approaches for their Studies
The formation of alpha-clusters in nuclei close to the decay thresholds is
discussed. These states can be considered to be boson-condensates, which are
formed in a second order phase transition in a mixture of nucleons and
alpha-particles. The de Broglie wavelength of the alpha-particles is larger
than the nuclear diameter, therefore the coherent properties of the
alpha-particles give particular effects for the study of such states. The
states are above the thresholds thus the enhanced emission of multiple-alphas
into the same direction is observed. The probability for the emission of
multiple-alphas is not described by Hauser-Feshbach theory for compound nucleus
decay.Comment: 21 pages, 12 figures
Elastic -transfer in the elastic scattering of OC
The elastic scattering OC angular distributions at O
bombarding energies of 100.0, 115.9 and 124.0 MeV and their optical model
description including the -particle exchange contribution calculated in
the Coupled Reaction Channel approach are presented. The angular distributions
show not only the usual diffraction pattern but also, at larger angles,
intermediate structure of refractive origin on which finer oscillations are
superimposed. The large angle features can be consistently described including
explicitly the elastic -transfer process and using a refractive optical
potential with a deep real part and a weakly absorptive imaginary part.Comment: 3 pages, 2 figures, accepted in Eur.Phys.J A (Short note
Complementary optical-potential analysis of alpha-particle elastic scattering and induced reactions at low energies
A previously derived semi-microscopic analysis based on the Double Folding
Model, for alpha-particle elastic scattering on A~100 nuclei at energies below
32 MeV, is extended to medium mass A ~ 50-120 nuclei and energies from ~13 to
50 MeV. The energy-dependent phenomenological imaginary part for this
semi-microscopic optical model potential was obtained including the dispersive
correction to the microscopic real potential, and used within a concurrent
phenomenological analysis of the same data basis. A regional parameter set for
low-energy alpha-particles entirely based on elastic-scattering data analysis
was also obtained for nuclei within the above-mentioned mass and energy ranges.
Then, an ultimate assessment of (alpha,gamma), (alpha,n) and (alpha,p) reaction
cross sections concerned target nuclei from 45Sc to 118Sn and incident energies
below ~12 MeV. The former diffuseness of the real part of optical potential as
well as the surface imaginary-potential depth have been found responsible for
the actual difficulties in the description of these data, and modified in order
to obtain an optical potential which describe equally well both the low energy
elastic-scattering and induced-reaction data of alpha-particles.Comment: 46 pages, 16 figures. n_TOF Collaboration Annual Meeting, Bari,
Italy, 28-30 November 2007
(http://www.cern.ch/ntof/Documents/bari_nov07/bari_slides.php); revised
version accepted for publication in ADND
Di-neutron elastic transfer in the 4He(6He,6He)4He reaction
Elastic He+He data measured at 15.9, and 60.3
MeV have been analyzed within the coupled reaction channels (CRC) formalism,
with the elastic-scattering and two-neutron () transfer amplitudes
coherently included. Contributions from the direct (one-step) and sequential
(two-step) -transfers were treated explicitly based on a realistic
assumption for the -transfer form factor. The oscillatory pattern observed
in He(He,He)He angular distribution at low energies was found
to be due to an interference between the elastic scattering and -transfer
amplitudes. Our CRC analysis shows consistently that the direct -transfer
strongly dominates over the sequential transfer and thus confirms the dominance
of 2He configuration over the He one in the He wave function.
This result suggests a strong clusterization of the two valence neutrons and
allows, therefore, a reliable estimate for the \emph{di-neutron} spectroscopic
amplitude.Comment: Accepted for publication in Phys. Lett.
A study of the almost sequential mechanism of true ternary fission
We consider the collinear ternary fission which is a sequential ternary decay
with a very short time between the ruptures of two necks connecting the middle
cluster of the ternary nuclear system and outer fragments. In particular, we
consider the case where the Coulomb field of the first massive fragment
separated during the first step of the fission produces a lower pre-scission
barrier in the second step of the residual part of the ternary system. In this
case, we obtain a probability of about for the yield of massive
clusters such as \nuclide[70]{Ni}, \nuclide[80-82]{Ge}, \nuclide[86]{Se}, and
\nuclide[94]{Kr} in the ternary fission of \nuclide[252]{Cf}. These products
appear together with the clusters having mass numbers of --. The
results show that the yield of a heavy cluster such as \nuclide[68-70]{Ni}
would be followed by a product of -- with a large probability as
observed in the experimental data obtained with the FOBOS spectrometer at the
Joint Institute for Nuclear Research. The third product is not observed. The
landscape of the potential energy surface shows that the configuration of the
Ni + Ca + Sn decay channel is lower about 12 MeV than that of the Ca + Ni + Sn
channel. This leads to the fact, that the yield of Ni and Sn is large. The
analysis on the dependence of the velocity of the middle fragment on mass
numbers of the outer products leads to the conclusion that, in the collinear
tripartition channel of \nuclide[252]{Cf}, the middle cluster has a very small
velocity, which does not allow it to be found in experiments.Comment: 11 pages, 9 figure
From the stable to the exotic: clustering in light nuclei
A great deal of research work has been undertaken in alpha-clustering study
since the pioneering discovery of 12C+12C molecular resonances half a century
ago. Our knowledge on physics of nuclear molecules has increased considerably
and nuclear clustering remains one of the most fruitful domains of nuclear
physics, facing some of the greatest challenges and opportunities in the years
ahead. The occurrence of "exotic" shapes in light N=Z alpha-like nuclei is
investigated. Various approaches of the superdeformed and hyperdeformed bands
associated with quasimolecular resonant structures are presented. Evolution of
clustering from stability to the drip-lines is examined: clustering aspects
are, in particular, discussed for light exotic nuclei with large neutron excess
such as neutron-rich Oxygen isotopes with their complete spectroscopy.Comment: 15 pages, 5 figures, Presented at the International Symposium on "New
Horizons in Fundamental Physics - From Neutrons Nuclei via Superheavy
Elements and Supercritical Fields to Neutron Stars and Cosmic Rays" held at
Makutsi Safari Farm, South Africa, December 23-29, 2015. arXiv admin note:
substantial text overlap with arXiv:1402.6590, arXiv:1303.0960,
arXiv:1408.0684, arXiv:1011.342
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